I used to use BIS with my 8100. I have now got a BES server on Exchange in the office. I contacted Orange who have put me on BES.
The phone functions (calls and sms) work fine.
I can only get email and calender to work when plugged into the BES via USB. Nothing works wirelessly. I had to activate when plugged in. If I send an email when plugged in it works. But when unplugged I get the message as above re blocked.